A half-toroidal continuously variable transmission such as disclosed in JP2003214516A, JP2007315595A, JP2008025821A, and JP2008275088A is used as an automobile transmission apparatus. Moreover, JP2004169719A discloses construction in which the range of adjustment of the transmission ratio is made wider by combining a toroidal continuously variable transmission and a planetary gear mechanism.
FIG. 2 illustrates a first example of conventional construction of a toroidal continuously variable transmission. In this first example of conventional construction, a pair of input-side disks 2a, 2b are supported around both end sections in the axial direction of an input rotating shaft 1 by a ball spline 18 so that one side surface in the axial direction of each, which are toroidal curved surfaces, face each other, and so that the disks 2a, 2b are able to move away from each other or closer to each other, and are able to rotate in synchronization with the input rotating shaft 1. An output cylinder 3 is supported around the middle section in the axial direction of the input rotating shaft 1 so as to be able to rotate with respect to the input rotating shaft 1. An output gear 4 is fastened around the center section in the axial direction of the outer-circumferential surface of the output cylinder 3, and a pair of output-side disks 5 are supported by a spline joint on both end sections in the axial direction of the outer-circumferential surface of the output cylinder 3 so as to be able to rotate in synchronization with the output cylinder 3. In this state, one side surface in the axial direction of each of the pair of output-side disks 5, which are toroidal curved surfaces, face one side surface in the axial direction of the input-side disks 2a, 2b. 
Plural power rollers 6, having convex spherical circumferential surfaces, are held between one side surface in the axial direction of one of the input-side disks 2a (disk on the left side in FIG. 2) and one side surface in the axial direction of one of the output-side disks 5, and between one side surface in the axial direction of the other input-side disk 2b (disk on the right side in FIG. 2) and one side in the axial direction of the other output-side disk 5. The power rollers 6 are supported by a trunnion 7 as a support member so as to be able to roll freely, and these rollers 6 roll as the input-side disks 2a, 2b rotate, and transmit power from the input-side disks 2a, 2b to the output-side disks 5. In other words, when the toroidal continuously variable transmission is operating, a drive shaft 8 rotates and drives one of the input-side disks 2a by way of a pressing device 9, which is a loading cam. As a result, the pair of input-side disks 2a, 2b that are supported on both end sections in the axial direction of the input rotating shaft 1 rotate in synchronization while being pressed in a direction toward each other. The rotation of the pair of input-side disks 2a, 2b is transmitted to the pair of output-side disks 5 by way of the power rollers 6, and obtained from the output gear 4.
In the case of the first example of conventional construction, pre-loaded springs 10a, 10b that are disc springs or the like having large elastic force are provided in positions near both ends in the axial direction of the input rotating shaft 1 so as to hold the pair of input-side disks 2a, 2b from both sides in the axial direction of the input rotating shaft 1. These pre-loaded springs 10a, 10b maintain the minimum required amount of surface pressure at areas of rolling contact (tractions sections) between the circumferential surfaces of the power rollers 6 and the one side surface in the axial direction of the input-side disks 2a, 2b and the output-side disks 5 even when the pressing device 9 is not operating (when the drive shaft 8 is stopped). With this kind of construction, the areas of rolling contact can start transmitting power immediately at the start of operation of the toroidal continuously variable transmission without a large amount of slipping occurring.
The elastic force for maintaining the minimum required amount of surface pressure at the areas of rolling contact is obtained by the pre-loaded spring 10a of the pre-loaded springs 10a, 10b that is arranged between one of the input-side disks 2a and one end in the axial direction of the input rotating shaft 1 (pressing device 9). The other pre-loaded spring 10b that is arranged between a loading nut 11 that is screwed onto the other end section in the axial direction of the input rotating shaft 1 (right end section in FIG. 2) and the other input-side disk 2b is for easing impact that is applied during sudden operation of the pressing device 9, and could be omitted. When the other pre-loaded spring 10b is provided, that pre-loaded spring 10b is given sufficiently large elastic force, or in other words, enough elastic force so as not to be completely pressed between the input-side disks 2a, 2b and the output-side disks 5 when transmitting large torque.
In the case of this kind of toroidal continuously variable transmission, the work of adjusting the elastic force of the one pre-loaded spring 10a in order to maintain the minimum required surface pressure at the areas of rolling contact is troublesome. More specifically, in the case of the first example of conventional construction, it is necessary to adjust the elastic force of the one pre-loaded spring 10a by changing the amount of tightening of the loading nut 11 that is screwed onto the other end section in the axial direction of the input rotating shaft 1, which is troublesome. In regard to this, JP2000205361A and JP2009041715 disclose construction in which a locking ring called a cotter is used instead of a loading nut.
FIG. 3 to FIG. 6 illustrate a second example of conventional construction in which this kind of locking ring is incorporated. In the case of this second example of conventional construction, a female spline section 12 is formed so as to cover the range from the middle section in the axial direction of the inner-circumferential surface of the input-side disk 2b to the other end section in the axial direction (right end section in FIG. 3 to FIG. 5), and a male spline section 13 is formed around the outer-circumferential surface of the other end section in the axial direction (portion near the right end in FIG. 3 and FIG. 4) of the input rotating shaft 1a, and this female spline section 12 fits with the male spline section 13. Moreover, a locking groove 14 is formed around the entire circumference of a portion of the outer-circumferential surface of the input rotating shaft 1a that is adjacent to the other end side (right side in FIG. 3 and FIG. 4) of the male spline section 13, and the inner half section in the radial direction of a locking ring 15 that is composed of plural (2 to 4) partial circular-arc shaped elements is locked into the locking groove 14. The outer half section in the radial direction of one end surface in the axial direction (left side surface in FIG. 3 and FIG. 4) of the locking ring 15 comes in contact with the inside-end section in the radial direction of the other end surface in the axial direction of the input-side disk 2b. 
The elastic force of the one pre-loaded spring 10a that is for maintaining the minimum required surface pressure at the areas of rolling contact between the circumferential surfaces of the power rollers 6 (see FIG. 2) and the one side surfaces in the axial direction of the input-side disks 2a, 2b when the hydraulic type pressing device 9a is not operating is adjusted by the thickness in the axial direction of the locking ring 15 (by selecting a locking ring having an appropriate thickness dimension in the axial direction). Moreover, a restraining ring 16 having a L-shaped cross section is fitted around the outside of the other end section in the axial direction of the input rotating shaft 1a in a portion that is adjacent in the axial direction of the input rotating shaft 1a to the other end side of the locking groove 14, and by causing that restraining ring 16 to come in direct contact with or to closely face the outer-circumferential surface of the locking ring 15, the plural elements of the locking ring 15 are prevented from coming out from the locking groove 14. The displacement of the restraining ring 16 in the axial direction of the input rotating shaft 1a is prevented by a retaining ring 17 that is locked in the other end section in the axial direction of the input rotating shaft 1a on the other end side in the axial direction of the input rotating shaft 1a of the restraining ring 16. In this second example of conventional construction, by using an integrated type output-side disk 5a, it is possible to make the overall toroidal continuously variable transmission more compact and lightweight. However, the construction and function of the integrated type output-side disk 5a is not related to the scope of the present invention, so an explanation here is omitted.
In the case of the toroidal continuously variable transmission of this second example of conventional construction, the other input-side disk 2b of the pair of input-side disks 2a, 2b that is arranged on the other end side in the axial direction of the input rotating shaft 1a elastically deforms during operation in a direction (axial direction) such that the portion near the outer diameter of the other input-side disk 2b moves toward the locking ring 15 side due to a force that is received from the power rollers 6 due to thrust that is generated by the pressing device 9 as exaggeratedly illustrated in FIG. 7. In other words, the force applied to the other input-side disk 2b due to thrust that is generated by the pressing device 9 during operation becomes a maximum during operation of the toroidal continuously variable transmission, and is tens of kN to hundreds of kN (several tF to tens of tF). Therefore, the amount of elastic deformation in the axial direction of the other input-side disc 2b due to force that is applied to the other input-side disk 2b due to thrust that is generated by the pressing device 9 during operation is several tenths of a mm (several 0.1 mm), which is an amount that cannot be ignored. When the other input-side disk 2b elastically deforms in the axial direction, rubbing occurs by continuous repeated contact between the other end surface in the axial direction of the other input-side disk 2b and one end surface in the axial direction of the locking ring 15, and there is a possibility that fletching wear will occur in the area of contact between the other end surface in the axial direction of the other input-side disk 2b and one end surface in the axial direction of the locking ring 15. Particularly, the position in the circumferential direction where the other input-side disk 2b elastically deforms constantly changes as the portion that is pressed by the power rollers 6 changes. Therefore, the frequency that rubbing occurs between the other end surface in the axial direction of the other input-side disk 2b and one end surface in the axial direction of the locking ring 15 becomes very high (about a hundred and several tens of Hz), and becomes a severe condition from the aspect of the occurrence of fletching wear.
Furthermore, in the case of this second example of conventional construction, a female spline section 12 is provided in the range from the middle section in the axial direction of the inner-circumferential surface of the input-side disk 2b to the other end section, so as the other input-side disk elastically deforms, rubbing occurs by continuous repeated contact between the edge of the other end in the axial direction (edge on the right end in FIG. 3 and FIG. 4) of the female spline groove of the female spline section 12 and one end surface in the axial direction (left side surface in FIG. 3 and FIG. 4) of the locking ring 15, and the edge on the other end in the axial direction of the female spline groove tries to bite into the one end surface in the axial direction of the locking ring 15. From this aspect, it can be said that fletching wear is easy to occur. Fletching wear is the starting point of damage such as pealing, and there is a possibility that the abrasion powder that is generated will contaminate the lubrication oil (traction oil), creating a poor lubrication state in all areas.